Functional role of forest diversity: Pros and cons of synthetic stands and across-site comparisons in established forests

In contrast to grasslands, forests have only rarely been the subject of functional biodiversity research. This paper addresses specific problems. which arise from applying the synthetic stand approach to long-lived plants, which can be taken to simulate the loss or addition of tree species or tree functional groups in forest stands. Planted synthetic stands often deviate from natural forests in several properties including trophic structure, tree age distribution, and horizontal and vertical canopy structures. Moreover, edge effects and the absence of a quasi-steady state in soil development limit the spectrum of processes which can be analysed for biodiversity effects in synthetic tree stands. We propose that these shortcomings can partly be overcome by combining the synthetic stand approach with observational Studies in existing forest stands of contrasting tree diversity. The potentials and limitations of comparisons among existing stands for functional biodiversity reseal-ell are briefly discussed using the example of the Hainich Tree Diversity Matrix, a species-rich temperate broad-leaved forest consisting of a small-scale mosaic of stands differing in tree diversity, which originated from a variety of historic forest-use practices. (C) 2008 Published by Elsevier GmbH oil behalf of Gesellschaft fur Okologie.